using System;

using System.IO;

using System.Security;

using System.Security.Cryptography;

using System.Runtime.InteropServices;

using System.Text;



namespace Lewis.SST.SecurityMethods

{

    /// <summary>

    /// Security class handles encryption/decryption for connection strings

    /// </summary>

    public class Security

    {

        /// <summary>

        /// Call this function to remove the key from memory after use for security.

        /// </summary>

        /// <param name="Destination"></param>

        /// <param name="Length"></param>

        /// <returns></returns>

        [System.Runtime.InteropServices.DllImport("KERNEL32.DLL", EntryPoint="RtlZeroMemory")]

        public static extern bool ZeroMemory(ref string Destination, int Length);



        /// <summary>

        /// Function to Generate 64 bit Key.

        /// </summary>

        /// <returns></returns>

        public static string GenerateKey()

        {

            // Create an instance of Symetric Algorithm. Key and IV is generated automatically.

            DESCryptoServiceProvider desCrypto = (DESCryptoServiceProvider)DESCryptoServiceProvider.Create();



            // Use the Automatically generated key for Encryption. 

            return ASCIIEncoding.ASCII.GetString(desCrypto.Key);

        }



        private Security()

        {

            // default ctor

        }



        /// <summary>

        /// static method to encrypt passed in string using passed in public key

        /// </summary>

        /// <param name="plainString"></param>

        /// <param name="sKey"></param>

        /// <returns></returns>

        public static string EncryptString(string plainString, string sKey)

        {

            DESCryptoServiceProvider DES = new DESCryptoServiceProvider();

            DES.Key = ASCIIEncoding.ASCII.GetBytes(sKey);

            DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey);

            String outstring = null;

            using (MemoryStream sEncrypted = new MemoryStream())

            {

                byte[] output = null;

                ICryptoTransform desencrypt = DES.CreateEncryptor();

                using (CryptoStream cryptostream = new CryptoStream(sEncrypted, desencrypt, CryptoStreamMode.Write))

                {

                    UTF8Encoding e = new UTF8Encoding();

                    byte[] bytearrayinput = e.GetBytes(plainString.ToCharArray());

                    cryptostream.Write(bytearrayinput, 0, bytearrayinput.Length);

                    cryptostream.FlushFinalBlock();

                    cryptostream.Close();

                }

                output = sEncrypted.ToArray();

                sEncrypted.Close();

                outstring = Convert.ToBase64String(output);

            }

            

            return  outstring;

        }



        /// <summary>

        /// static method to decrypt passed in string using passed in public key

        /// </summary>

        /// <param name="encryptedString"></param>

        /// <param name="sKey"></param>

        /// <returns></returns>

        public static string DecryptString(string encryptedString, string sKey)

        {

            DESCryptoServiceProvider DES = new DESCryptoServiceProvider();

            DES.Key = ASCIIEncoding.ASCII.GetBytes(sKey);

            DES.IV = ASCIIEncoding.ASCII.GetBytes(sKey);

            string outstring = null;

            using (MemoryStream sDecrypted = new MemoryStream())

            {

                try

                {

                    byte[] output = null;

                    UTF8Encoding e = new UTF8Encoding();

                    ICryptoTransform desdecrypt = DES.CreateDecryptor();

                    using (CryptoStream cryptostream = new CryptoStream(sDecrypted, desdecrypt, CryptoStreamMode.Write))

                    {

                        byte[] bytearrayinput = Convert.FromBase64String(encryptedString);

                        cryptostream.Write(bytearrayinput, 0, bytearrayinput.Length);

                        cryptostream.FlushFinalBlock();

                        cryptostream.Close();

                    }

                    output = sDecrypted.ToArray();

                    sDecrypted.Close();

                    outstring = e.GetString(output);

                }

                catch //(CryptographicException cex)

                {

                    // nop 

                }

            }

            return outstring;

        }

    }

}